The present relates to an improvement of an orientation control film of a liquid crystal cell employing ferroelectric liquid crystal materials.
Meyer, et al. found that some of the smectic liquid crystals (SmC*, SmH*) exhibited ferroelectricity (cf. J. de Phys., 36, L69 (1975)). Clark, et al. disclosed an application of ferroelectric liquid crystal materials to a liquid crystal display device and reported that these liquid crystal materials showed quick response of 1 ms or below (cf. Appl. Phys. Lett., 36, 899 (1980) and U.S. Pat. No. 4,367,924). From the technical viewpoint, it is most important for these cells to align ferroelectric liquid crystal molecules in a preferred direction substantially parallel to the substrate. According to U.S. Pat. No. 4,367,924, the above-mentioned alignment is obtained by applying a strong magnetic field or a shear stress. However, uniform alignment of liquid crystal molecules is hard to obtain for a cell comprising liquid crystal layers of several .mu.m or below in thickness, even by applying a significantly strong magnetic field. Even if it is possible, the process would not be suitable for mass production. The same is true for the application of a shear stress.
European Patent Application No. 91661 discloses a ferroelectric liquid crystal display device employing a rubbed orientation control film of an organic polymer (PIQ; polyimidoisoindoloquinazolinedione, a product of Hitachi Chemical Co., Ltd.) for achieving uniform alignment. The alignment process thereof comprises converting the ferroelectric liquid crystal into an isotropic phase and, while applying a strong electric field, cooling slowly, so that the process is not preferable for mass production.